The invention relates generally to a transceiver system, more particularly, to a single-ended to differential transconductor circuit in a transceiver system.
In a radio transceiver system, a single-ended signal is received from an antenna. To obtain balanced signals, a single-ended signal is converted to balanced differential signals. Typically, a balanced/unbalanced (Balun) circuit is used to convert an unbalanced single-ended signal to balanced differential signals.
A single-ended signal, generally an AC signal, is input in a balanced/unbalanced (Balun) circuit. An input signal travels about above and below the ground (0 V). Typically, it is desired to reference an input signal to ground (0 V) in a Balun circuit as it eliminates the needs of additional DC power supplies. However, a ground level voltage is not stable and often varies, which causes AC signals to vary in a very unpredictable way. To solve this problem, additional DC power supplies, such as a single DC power supply or dual DC power supplies, are often used to shift the ground reference voltage level to a stable DC voltage level. As a result, extra DC power supplies have to be used, thereby making a transceiver system large in size and much more expensive.
Another problem in the past is that a typical Balun circuit, such as an Op-Amp, has a low output impedance. The low output impedance generally interferes with a circuit to which the Balun circuit is connected.
It is with respect to these and other considerations that the present invention has been made.
In accordance with this invention, the above and other problems were solved by providing a single-ended to differential transconductor or conversion circuit to generate balanced differential output current signals and/or balanced differential output voltage signals from a single-ended input voltage signal.
In one embodiment of the present invention, the conversion circuit is capable of converting a single-ended input voltage signal to balanced differential signals, wherein an input voltage signal is referenced to ground (zero voltage) and travels both above and below the ground. The conversion circuit includes a pair of feedback circuits, having a plurality of transistors and a plurality of resistances, disposed and coupled in a mirror image, to boost an input impedance to an output impedance of a gain of one of the transistors, to isolate an output load from an input of the conversion circuit, and to provide a voltage gain from the input to an output of the conversion circuit determined by the plurality of resistances.
In one embodiment, a circuit for converting a single-ended input signal to differential output signals in accordance with the principles of the present invention includes a first feedback circuit having first and second transistors disposed in series; an input port, coupled to the first transistor, to receive the single-ended input signal; a first shunt voltage node, disposed between the first and second transistors, to receive a shunt feedback which buffers the single-ended input signal to the first shunt voltage node; and an output port to output one of the differential output signals. The circuit also includes a second feedback circuit having third and fourth transistors disposed in series; an input port, coupled to the third transistor, to connect to the ground; a second shunt voltage node, disposed between the third and fourth transistors, to receive a shunt feedback which buffers a ground voltage to the second shunt voltage node; and an output port to output the other differential output signal.
Still in one embodiment, the circuit in accordance with the principles of the present invention further includes a first resistance disposed between the first shunt voltage node and the second shunt voltage node; a first current source coupled to the first and second transistors; a second current source coupled to the first shunt voltage node; a third current source coupled to the third and fourth transistors; a fourth current source coupled to the second shunt voltage node; a second resistance coupled to the first output port and the second transistor; and a third resistance coupled to the second output port and the fourth transistor.
In one embodiment, a transceiver system in accordance with the principles of the present invention includes an antenna for receiving a single-ended input signal; a bandpass filter to filter out noise received from the antenna; a transceiver to recover the received input signal from before the signal is transmitted; and an antenna interface coupled between the bandpass filter and the transceiver. The antenna interface includes a conversion circuit to convert the single-ended input signal to differential output signals. The circuit includes a first feedback circuit having first and second transistors disposed in series; an input port, coupled to the first transistor, to receive the single-ended input signal; a first shunt voltage node, disposed between the first and second transistors, to receive a shunt feedback which buffers the single-ended input signal to the first shunt voltage node; and an output port to output one of the differential output signals. The circuit also includes a second feedback circuit having third and fourth transistors disposed in series; an input port, coupled to the third transistor, to connect to the ground; a second shunt voltage node, disposed between the third and fourth transistors, to receive a shunt feedback which buffers a ground voltage to the second shunt voltage node; and an output port to output the other differential output signal.
Still in one embodiment, the conversion circuit further includes a first resistance disposed between the first shunt voltage node and the second shunt voltage node; a first current source coupled to the first and second transistors; a second current source coupled to the first shunt voltage node; a third current source coupled to the third and fourth transistors; a fourth current source coupled to the second shunt voltage node; a second resistance coupled to the first output port and the second transistor; and a third resistance coupled to the second output port and the fourth transistor.
Further in one embodiment, a gain of the conversion circuit is determined by the first, second, and third resistances.
Yet in one embodiment, an output impedance of the conversion circuit is determined by the gain of the first transistor.
Accordingly, additional DC power supplies for a DC voltage level shift can be eliminated in the present invention. Further, external pins can be reduced. Furthermore, a high output impedance is provided in the present invention such that the interference to a connected circuit can be significantly reduced. The conversion circuit of the present invention having a high output impedance can be readily adopted by a test equipment.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.